PETROGRAPHY, STRATIGRAPHY AND WEATHERING OF LATE PLEISTOCENE TILLS IN EAST YORKSHIRE, LINCOLNSHIRE AND NORTH NORFOLK

Abstract

SUMMARY A study of the vertical and lateral variations in particle size distribution, mineralogy and other petrographic features of tills in East Yorkshire, Lincolnshire and north Norfolk shows that the Devensian glacial succession in eastern England contains only two tills, for which the new names Skipsea and Withernsea Tills are proposed. The “Hessle Till”, recognised as a third member by most previous workers, is shown to be the postglacial (Flandrian) weathering profile on whichever of these two occurs at the surface. South of Flamborough Head, the upper (Withernsea) till occurs on land only in an arcuate area adjoining the coast of south-east Holderness. The Skipsea Till occupies the whole of Holderness, and extends westwards on to the lower dip-slope of the Wolds and southwards to the northern coastal strip of Norfolk, where in its weathered form it has previously been known as the Hunstanton Till. These conclusions agree with those reached by Bisat forty years ago, but hitherto unpublished. The weathering of the tills involves decalcification, the softening and disaggregation of sandstone, shale, igneous and metamorphic erratics, clay alteration and translocation, and the alteration of micas and some heavy minerals in the sand and silt fractions. Reddish brown colours, previously regarded as characteristic of the “Hessle Till”, result from oxidation of pyrite and siderite to depths of approximately 5 m.